In the past, metal corrosion caused by conventional motor fuels such as gasoline was not much of a problem because such hydrocarbon fuels are inherently non-corrosive. However, with the advent of fuels containing alcohols such as gasohol or straight alcohol fuels, corrosion has become a major problem because such fuels are corrosive. It has been reported that this corrosion is due to the presence of acidic contaminants in such fuels such as formic acid. It is almost impossible to avoid such contaminants because they occur in fuel grade alcohols and are also found in storage as normal alcohol oxidation products.
It is known from U.S. Pat. No. 4,305,730 that polymerized linoleic acid, especially trimer, is an effective corrosion inhibitor for alcohol-type motor fuels. It has now been discovered that the corrosion inhibiting properties of such polymerized polyunsaturated aliphatic monocarboxylic acids are improved by use of the co-additives described herein. The substituted imidazoline co-additives of the invention, more fully described hereafter, also are known compounds which heretofore have found use, for example, in motor fuel compositions to prevent carburetor icing as disclosed in U.S. Pat. No. 3,036,902.